1. Field of the Invention
The present invention relates to a rotary drier for drying semiconductor substrates or, glass plates for liquid crystal and so on (hereinafter simply referred to as "wafers"), used in the step of drying during manufacturing the wafers. More specifically, the present invention relates to a rotary drier for drying wafers by swishing off liquid drops on the wafers by using centrifugal force.
2. Description of the Related Art
A rotary drier of wafers of interest to the present invention is disclosed in, for example, U.S. Pat. No. 4,677,759. Present FIG. 1 is a perspective view of a rotor which constitutes a main portion of the rotary drier of wafers disclosed in such patent. Referring to present FIG. 1, a conventional rotary drier of wafers comprises a rotor 1 which is rotated in the direction of the arrow in the figure. The rotor 1 comprises a turntable 4 and opposing wall portions 2a and 2b provided on the turntable 4. Pairs of support axes 10a and 10b are provided on opposing positions of the respective wall portions 2a and 2b. The support axes 10a and 10b support a pair of cradles 5a and 5b housing wafers to be dried. When the rotor 1 is in a static state, the pair of cradles 5a and 5b are kept in the state shown at A in the figure. More specifically, the receiving inlet 6 of each of the cradles 5a and 5b is facing upward for receiving wafers to be dried. A plurality of wafers W contained in cassettes 8a and 8b (FIG. 2), which will be described later, are introduced into the cradles 5a and 5b, which wafers were previously subjected to wet surface treatment.
FIG. 2 is a cross-sectional view of a main portion of the rotor shown in FIG. 1 in the rotating state. Referring to FIG. 2, the rotor 1 is rotated as the turntable 4 is rotated by a turntable driving motor 29 provided therebelow. When the rotor 1 is being rotated, the cradles 5a and 5b are kept in the state shown at B in the figure by the centrifugal force. In this state, the plurality of wafers W held in the cassettes 8a and 8b are maintained approximately horizontal and, consequently, the drops on the surfaces of the wafers W are swished off by the centrifugal force.
FIG. 3 is an enlarged view of the portion shown by the numeral III of FIG. 2. Referring to FIG. 3, the turntable 4 of the conventional rotary drier of wafers comprises an upper plate 4a for supporting the wall portions 2a and 2b, a lower plate 4b for transmitting the rotating force of the turntable driving motor 29 to the turntable 4, and a support 4c for connecting the upper and lower plates 4a and 4b. The rotating force of the turntable driving motor 29 is transmitted to the turntable 4 through a rotary driving axis 28. The lower plate 4b of the turntable and the rotary driving axis 28 are connected with each other by means of a plurality of fixing bolts 32. A cap 31 is provided thereon.
The conventional rotary drier of wafers is structured as described above. The outer dimension of the cassettes 8a and 8b is different dependent on the diameter of the wafers W (4 to 8 inch) to be dried. Therefore, when the wafers W having a different diameter are to be subjected to the step of drying, the pair of cradles 5a and 5b housing the cassettes 8a and 8b must be correspondingly changed so that the turntable 4 as a whole is well balanced during rotation.
In the conventional rotary drier of wafers, the wafers W are dried while maintained at a horizontal attitude for swishing off water by the centrifugal force, as shown in FIG. 2. Since a great centrifugal force is applied to the cradle 5, it has been a general understanding that the cradle and the turntable rotatably supporting the same must be an integral durable structure. In addition, since a great centrifugal force is applied to swingable support axes 10a and 10b for integrally supporting the cradles 5 on the wall portions 2a and 2b of the turntable 4, it was thought necessary that the cradles 5a and 5b be integral with the support axes 10a and 10b.
For the above-described reasons, in a conventional rotary drier of wafers, an attaching/detaching mechanism such as a fixing bolt 32 is provided between the turntable 4 and the rotary driving axis 28 for rotating the turntable 4, as shown in FIG. 3. When wafers W having a different diameter are to be dried, not only the cradles 5a and 5b housing the wafers W but the rotor 1 itself is changed to another rotor 1 having a pair of cradles 5a and 5b of different size.
Accordingly, a conventional rotary drier of wafers has the following drawbacks.
(1) A plurality of rotors 1 having cradles 5 of different outer dimensions corresponding to the diameters of differently-sized wafers W must be prepared, which increases the cost of the rotary drier of wafers. PA1 (2) Referring to FIG. 3, the so called "fit" dimension d between a hole provided on the lower plate 4b of the turntable 4 and a concave portion of the rotary driving axis 28 is tight (near tight fit) in order to prevent deviation of the centers of these portions. Therefore, it was very hard to change the rotor 1, which is relatively heavy (e.g. about 20 kg).